Move ALLOC_CACHE_ALIGN_BUFFER() to the new memalign.h header

Now that we have a new header file for cache-aligned allocation, we should
move the stack-based allocation macro there also.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/board/raspberrypi/rpi/rpi.c b/board/raspberrypi/rpi/rpi.c
index d21750e..6d7be11 100644
--- a/board/raspberrypi/rpi/rpi.c
+++ b/board/raspberrypi/rpi/rpi.c
@@ -10,6 +10,7 @@
 #include <fdt_support.h>
 #include <fdt_simplefb.h>
 #include <lcd.h>
+#include <memalign.h>
 #include <mmc.h>
 #include <asm/gpio.h>
 #include <asm/arch/mbox.h>